Effects of Extractives from Pressure-Refined Hardwood Fiber on the Gel Time of Urea-Formaldehyde Resin

Pressure-refined chips (bark included) of the five major low-grade southern hardwood species were sequentially extracted with benzene, ethanol, and water. The five species were southern red oak, sweetgum, white oak, mockernut hickory, and black tupelo. The amount of each extractive and their effects on the gel time of catalyzed urea-formaldehyde resin were determined. The major constituents of the total extractives were the ethanol (6.5 percent to 12.5 percent) and water-soluble (3.2 percent to 8.5 percent) extractives. Generally, both these soluble extractives had a significant effect on resin gel time. The ethanol-soluble extractives decreased the gel time as much as 41 percent, and the water-soluble extractives increased the gel time in excess of 65 percent. Further research is needed to reveal reasons for the effects of these extractives and their influence on the properties of a fiberboard product.

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